Apparatus for making tubular camshaft assemblies

ABSTRACT

Camshaft assemblies, methods and apparatus are provided for making camshafts by the expansion of tubular shafts into prelocated cams, journals and other elements, if desired. Features of the camshafts include trilobe or polylobe element openings, preferably splined or serrated for low energy filling and high torque capacity and high strength low alloy mild steel tubular shaft material. The method emphasizes trapping, or loading, the shaft to prevent axial lengthening during expansion such as by mechanical ballizing. The apparatus includes adjustable thrust blocks and locating plungers with incorporated flush pin gages together with hydraulic or other loading means all for use in carrying out the assembly method with various benefits from the incorporated features.

This is a division of application Ser. No. 23,320 filed on Mar. 9, 1987,now abandoned.

TECHNICAL FIELD

This invention relates to camshafts for internal combustion engines andthe like. In particular, the invention relates to assembled camshaftsand to methods and apparatus for their manufacture.

BACKGROUND

U.S. Pat. No. 4,597,365, issued July 1, 1986 to the assignee of thepresent invention, discloses a camshaft assembly and method involvingretention of cam and journal elements on a hollow shaft by expansion ofthe shaft into engagment with preshaped openings of the elements.Various other camshaft assemblies and methods are also shown by theprior art. While certain of these arrangements provide benefits ineconomy and structure, further economies are desirable for making themost efficient use of this technology.

SUMMARY OF THE INVENTION

The present invention provides improved camshaft assemblies,manufacturing procedures and equipment which yield benefits in bothstructural soundness and economy of manufacture for assembled camshafts,particularly of the type described in the noted U.S. Pat. No. 4,597,365,the disclosure of which is incorporated herein by reference.

An improved camshaft according to the invention includes the use ofnonround element openings comprising so called curved polygons ofpreferably uniform diameter and having odd numbers of slightly eccentriclobes. These configurations minimize the energy required for theirfilling by expansion of the associated hollow shaft while providing ajoint of high torque capacity. The addition of one or more small groovesor splines on the ends of the lobes further improves the torquecapacity. By use of preferred materials for the shaft, the torsionalstrength relative to the expansion energy required may be furtherimproved.

In the manufacturing process, control of the length and straightness ofthe assembly and the ease of its removal from the assembly fixture areaided by the added step of loading the hollow shaft from the initiallyexpanded (front) end during the mechanical expansion procedure so as toprevent its lengthening and locking itself in the fixture.

In the assembly apparatus, the use of adjustable locator blocks andspring loaded guide pin plungers assists in accurately locating the camelements in their proper angular positions on the shaft prior to theirbeing locked in position by shaft expansion. In addition, the guide pinsmay have stepped heads cooperating with external gaging surfaces of thefixture to permit visual or mechanical indication of proper or improperpositioning of the cams and their presence in the fixture duringassembly.

These and other features and advantages of the invention will be morefully understood from the following description of certain embodimentsof the invention taken together with the accompanying drawings.

BRIEF DRAWING DESCRIPTION

In the drawings:

FIG. 1 is a pictorial view of a portion of an internal combustion enginecamshaft assembly formed in accordance with the invention;

FIG. 2 is a transverse cross-sectional view of a portion of the camshaftassembly from the plane indicated by the line 2--2 of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of a portion of thecamshaft assembly from the plane indicated by the line 3--3 of FIG. 2;

FIG. 4 is a pictorial view of a separate cam element prior to assemblyand having a trilobe opening according to the invention with inwardlysplined lobes;

FIG. 5 is a graphical presentation of the development of a trilobeconfiguration having uniform diameters according to the invention;

FIG. 6 is a pictorial view showing a novel assembly apparatus andfixture for assembling camshafts according to the invention;

FIG. 7 is a diagramatic pictorial view of portions of the novelapparatus for mechanically loading the shaft during the course ofcamshaft assembly by a process in accordance with the invention;

FIG. 8 is a pictorial view similar to a portion of FIG. 6 and showing analternative apparatus for hydraulically loading the shaft;

FIG. 9 is a transverse cross-sectional view from the plane indicated bythe line 9--9 of FIG. 6; and

FIGS. 10a-10e are fragmentary cross-sectional views illustrating variouspositions of the flush pin gages.

DETAILED DESCRIPTION

Referring now to the drawings in detail, numeral 10 generally indicatespart of a finished camshaft assembly formed in accordance with theinvention. Camshaft 10 includes a hollow supporting tube or shaft 11which which has been expanded in a manner to be subsequently described.

While the shaft may be made of ordinary low carbon steel as noted inU.S. Pat. No. 4,597,365, we prefer to make the shaft 11 of a mild steelof High Strength Low Allow specification such as SAE 1022 HSLA. Thesteel tubing used to make the shaft may be of a type which is electricresistance welded and drawn over a mandrel, having a yield strength of45,000-55,000 psi.

Fixedly positioned on the tube 11 are a plurality of cam elements 12 andjournal elements 14. Additional elements such as gears, eccentrics orsprockets could also be included if desired. The elements 12, 14 arelongitudinally spaced and the cam elements 12 are angularly oriented inpredetermined positions for actuating valve gear in an internalcombustion engine or the like. The cam elements 12 are preferably forgedand hardened, either fully or on their wearing surfaces, and the journalelements 14 may be similarly formed or, if desired and their operationpermits, may be formed of non-hardened material.

The forged, or otherwise formed, cam and journal elements are providedwith tube or shaft receiving openings 15, which are preferablynon-circular to positively lock onto the shaft when it is expanded intothe openings. We have found that a preferred shape or configuration forthe openings is that of a so-called curved polygon of preferablyuniform, or essentially uniform, diameter. Such curved polygons may bemade with any odd number of lobes, however we prefer to use and haveobtained good results using a configuration, which we call a trilobe,having three eccentric lobes 16.

Minimal eccentricity is required and preferred for high torque capacitywith a minimum of expansion energy. An eccentricity of only fivethousandths of an inch (0.005 in. difference in radial height betweenthe lobes and adjacent valleys) gives good results although greatereccentricities can be used if desired.

To further increase the torque capacity, the addition of one or moresmall serrations or splines 17, preferably at the ends of the lobes, isalso desirable. We have found effective the addition of nine inwardlyprotruding and longitudinally extending splines 17. These splines arepreferably arranged in closely spaced groups of three at the end of eachof the lobes 16 of the openings 15. The splines protrude inwardly onlyabout 0.005 inches, or approximately equal to the preferred trilobeeccentricity. The addition of these splines was found to increase thebreakaway torque for the shaft mounted trilobe elements about 20-25percent. FIG. 4 illustrates a cam element 12 prior to assembly andhaving the preferred nine splined trilobe opening previously described.Obviously, in this and the previous views, the eccentricity of theopening is grossly exaggerated for clarity of illustration as it wouldbe almost unnoticeable if drawn in its true configuration.

In FIG. 5, a graphical illustration of the development of a trilobefigure is presented having an eccentricity 18 measured from a circle 19defining the minimum radius of the trilobe perimeter 20. The developedperimeter 20 is made up of blended tangent swing radii in the form of aseries of alternating long arcs 22 and short arcs 23 which are drawnfrom three equally spaced centers 24 spaced about the true center 25 ofthe figure. The result is that the perimeter has an overall uniformheight or width 26 in any direction. For simplicity, this is generallyreferred to as a uniform diameter 26 although it should be understoodthat this uniform diameter dimension passes sequentially through each ofthe three centers 24 and only passes through the true center 25 when thediameter is at the midpoints of two opposing long and short arcs 22, 23.

Assembly Apparatus

Referring now to FIGS. 6-10 there are shown various constructionfeatures of a fixture generally indicated by numeral 27 and particularlyadapted for the manufacture of camshafts according to the invention.Fixture 27 includes a base 28 on which are fixedly mounted a series ofalternately disposed locators 30 and spacers 31 longitudinally alignedand sandwiched between a rear stop block 32 and a movable front backupblock 34 adjacent to a fixed front carrier block 35. A movable cover 36is also provided.

The spacers 31 separate the journals 14, cams 12 and other elements, ifany, to maintain their proper axial locations. The locators 30 supportthe elements with their openings 15 in alignment and the lobes of thecam elements in their proper angularly indexed positions. Precisionground locator blocks 38 may be provided on each of the cam locators toangularly position their respective cams within any desired tolerences.The blocks 38 may be individually ground or shimmed for adjustment toobtain the desired accuracy. Other means, such as wedges or screws mightbe substituted for, or used together with, the locator blocks 38 ifdesired.

To insure that each cam lobe is firmly held in its locator against itslocator block 38, suitable positioning devices may be provided, such asthe spring biased guide pins or plungers 39 best shown in FIG. 9. Theplungers 39 may be mounted in the cover 36 as shown or, if needed, maybe positioned along a side or the bottom in one of the locators toproperly position their respective cams. The plungers 39 are providedwith heads 40 having stepped ends 42 that cooperate with the adjacentouter surfaces of the cover or other member to act as flush pin gages.These gages may be inspected visually or by touch or may be contacted byprobes at an inspection station, such as when used in a travelingfixture pallet in high volume manufacture.

FIGS. 10a-10e illustrate various positions of the flush pin gages andtheir indications, such as:

FIG. 10a shows a gage positioned too high, indicating the presence of anelement that is too large or a cam lobe not properly positioned againstits locator;

FIG. 10b shows the lower step flush, indicating a cam or other elementat the upper tolerance limit;

FIG. 10c shows the gage centered, indicating an element in the midtolerance range;

FIG. 10d shows the upper step flush, indicating an element at the lowtolerance limit; and

FIG. 10e shows a gage position too low, indicating a too small ormissing element.

FIGS. 7 and 8 show in further detail certain features of the assemblyapparatus including alternative means for end loading the shaft duringassembly.

FIG. 7 shows the rear end 43 of the shaft and the associated rearjournal 14 lying against the rear stop block 32. Similarly, the frontend 44 of the shaft and the associated front journal 14 are engaged by ahardened backup bushing 46 carried by the backup block 34. A hollowscrew actuator 47, threaded into the carrier block 35 comprisesmechanically actuated means for exerting force through the backupbushing on the front end 44 of the shaft 11 to load the shaft duringassembly. Also shown are a ball 48 and cupped rod 50 actuated bysuitable means, not shown, to force the ball through the shaft duringassembly.

FIG. 8 illustrates a fixture whereby the front end 44 of the shaft 11 issimilarly loaded through a backup bushing 46 carried by a backup block34. However, the shaft loading means comprises a hydraulic cylinder 51threaded into the carrier block 35 and having a hydraulically actuatedhollow piston 52 that engages the backup bushing to apply the loadingforce to the shaft 11.

Assembly Method

The manufacture of a camshaft assembly in accordance with the inventionis in many ways similar to that described in the noted U.S. Pat. No.4,597,365, although including significant differences in the followingpreferred steps:

(1) The elements, such as cams and journals, a gear, eccentric andsprocket or the like, are made with, or provided with, the preformedshaft openings 15 and are formed to relatively close, but normallyunfinished, dimensions. In accordance with the invention, the openingsare preferably nonround curved polygons of minimal eccentricity,preferably trilobes having one or more inwardly projecting splines 17 atthe lobe ends. Additionally, grooves or serrations extending outwardlyfrom or into the trilobe surface, or other variations, may be used.

The trilobe or other odd lobed curved polygon shape requires lowerenergy for filling by tube expansion while giving high breakawaytorques. Displacement of material from the valleys into the adjacentlobes with a minimum of expansion due to the preferred constantdiameter, or height, of the polygon eccentric perimeter is believed tobe an advantage of this configuration that leads to the lower energyrequirement.

(2) A tubular shaft 11 is provided, preferably made of high strength lowalloy mild steel such as SAE 1022 HSLA. The tube may be of theresistance welded type, sized by drawing over a mandrel and having ayield strength of 45,000-55,000 psi. This low yield strength combineswith significant work hardening after yielding to provide low expansionenergy with significantly higher breakaway torques after assembly thanother materials. The shaft outer diameter is circular and sized to fitclosely but freely within the eccentric shaft openings 15 of theelements 12, 14, etc. The dashed line 53 in FIGS. 2 and 4 represents theshaft outer diameter before expansion. Camshafts have been made withshafts of 3/4, 7/8 and 1 inch outer diameters but other sizes includinglarger and smaller diameters could be utilized if desired.

(3) The cam, journal and other elements, if any, are positioned in afixture such as fixture 27 with their openings 15 aligned on a commonaxis. The fixture may be similar to, but preferably differs from, thatdescribed in the noted U.S. Pat. No. 4,597,365 in various ways,including the construction of the locators and spacers and the additionof the locating and gaging means and the shaft end loading meanspreviously described.

(4) The fixture is closed, holding the elements in position and theshaft is inserted into the openings 15 in a predetermined longitudinalposition. The shaft ends are then loaded by hydraulic, mechanical orother force applying means with a force sufficient to preventsubstantial longitudinal growth of the shaft during the subsequentsteps.

(5) The shaft is expanded in any suitable manner. We prefer mechanicalexpansion by a ball 48 forced through the tube or shaft 11 from one end,called the front end 44, to the other, called the rear end 43. With thisprocess, sometimes known as ballizing, a uniformly sized smooth interior54 is formed within the tube.

The ball is preferably large enough to expand the tube into fullengagement with the element openings 15 and radially beyond the openingsbetween the elements, as is shown clearly in FIG. 3, so that theelements are permanently fixed in their established positions, bothangularly and longitudinally. In an embodiment wherein the initialclearance between the trilobe openings 15 and the shaft 11 beforeexpansion was 0.008 inches on the diameter and the trilobe eccentricitywas the preferred 0.005 inches, the use of a ball 48, oversize by 0.035inches relative to the initial inner diameter of the shaft 11, providedthe desired results with a minimum amount of expansion energy requiredrelative to the high level of breakaway torque obtained for theassembled cam elements.

However, in some cases greater trilobe eccentricities may be desirableas, for example, when wide journal or cam elements are used and morevolume for displacement of the expanded shaft material is required toavoid excessive longitudinal carryover of the displaced material.Trilobe openings with from 0.005 to 0.020 inch eccentricity have beentested but other dimensions could also be used as desired.

(6) After expansion of the shaft, the end loading of the shaft isreleased by backing off the force applying means. The assembled camshaftis then removed from the fixture for other finishing steps, if any,which may be required, such as hardening of the cams if they are notprehardened, grinding of the cams and journals, etc.

The force of the end loading of the shaft by the backup bushing 46acting in opposition to the stop block 32 should be sufficient toprevent significant longitudinal growth of the shaft 11 duringballizing. This causes all the growth to be radial and provides thepreferred complete filling of the trilobe openings 15 and the furtherexpansion of the shaft material radially beyond the openings 15 in thespaces located longitudinally between the elements 12, 14, etc. Inaddition, the end loading prevents the elements from being lockedagainst the spacers by lengthwise growth of the shaft during ballizingand, thus, after release of the end loading, allows easy removal of theassembled camshaft 10 from the fixture 27. Bending and other damagewhich might otherwise result from forced removal are thereby avoided.

Advantages

From the forgoing description of certain preferred embodiments of animproved camshaft assemblies, assembly apparatus and assembly methods itis seen that the various features of the invention provide numerousadvantages including:

more accurate axial location of cam, journal and other elements on theshaft;

higher breakaway torques with minimal thrust energy for forcing the ballthrough the tubular shaft by reason of improved splined trilobe or othercurved polygon shaped openings, improved shaft material selection, andend loading the shaft to prevent axial growth;

ease of removal from the fixture through prevention of axial growth;

better angular indexing by adjustable locators and locating plungers;and

loaded fixture inspection with flush pin gages carried on the locatingplungers.

While the invention has been described by reference to certain preferredembodiments, it should be understood that numerous changes could be madewithin the spirit and scope of the inventive concepts described.Accordingly it is intended that the invention not be limited to thedisclosed embodiments, but that it have the full scope permitted by thelanguage of the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. Apparatus for assemblinga multipiece camshaft, said apparatus comprisinglocating means forholding a plurality of hollow cam and journal elements in predeterminedfixed orientation and spacing with central openings aligned on a commonaxis, positioning means including a stop for axially locating one end ofa hollow shaft extending through the openings of said elements, forceapplying means engageable with an opposite end of the hollow shaft andoperable to load the shaft against the stop with a force adequate toprevent substantial axial growth of the shaft during subsequentexpansion, and means for mechanically expanding the shaft intomechanical interference engagement with all the element openings tosecure the elements permanently onto the shaft in said predeterminedorientation and spacing.
 2. Apparatus as in claim 1 wherein saidlocating means include locators recessed to receive and support theelements in desired lateral and angular orientations and spacers betweenthe locators to longitudinally separate and locate the elements, thelocators for the cam elements further including adjustable locator meansin the recesses and engageable with the cam lobes to accurately adjustthe desired angular location of the cam elements.
 3. Apparatus as inclaim 2 wherein said locating means further include biasing devicesengageable with the cam elements to urge them against their respectiveadjustable locator means.
 4. Apparatus as in claim 3 wherein the biasingdevices comprise resiliently urged guide pins and said pins incorporateends having stepped surfaces cooperating with adjacent surfaces of theapparatus to act as flush pin gages indicating the condition of elementsloaded into the apparatus.
 5. Apparatus as in claim 1 wherein the forceapplying means includes a hydraulic actuator for transmitting theapplied force.
 6. Apparatus as in claim 5 wherein the force applyingmeans further includes a hardened hollow bushing engageable with saidshaft opposite end and carried in a movable backup block fortransmitting to the shaft forces applied by the hydraulic actuator. 7.Apparatus as in claim 1 wherein the force applying means includes amechanical actuator for transmitting the applied force.
 8. Apparatus asin claim 7 wherein the force applying means comprises a screw actuator.9. Apparatus as in claim 8 wherein the force applying means furtherincludes a hardened hollow bushing engageable with said shaft oppositeend and carried in a movable backup block for transmitting to the shaftforces applied by the screw actuator.
 10. Apparatus for making tubularshaft assemblies, said apparatus comprisinglocating means for holding aplurality of hollow elements in fixed orientation and spacing withcentral openings aligned on a common axis, positioning means including astop for axially locating one end of a hollow shaft extending throughthe openings of said elements, force applying means engageable with anopposite end of the hollow shaft and operable to load the shaft againstthe stop with a force adequate to prevent substantial axial growth ofthe shaft during subsequent expansion, and means for mechanicallyexpanding the shaft into mechanical interference engagement with all theelement openings to secure the elements permanently onto the shaft insaid fixed orientation and spacing.
 11. Apparatus as in claim 10 whereinsaid locating means include locators recessed to receive and support theelements in desired orientations and spacers between the locators tolongitudinally separate and locate the elements, the locators forcertain elements further including adjustable locator means in therecesses and engageable with said certain elements to accurately adjustthe desired angular location thereof.
 12. Apparatus as in claim 11wherein said locating means further include biasing devices engageablewith said certain elements to urge them against their respectiveadjustable locator means.
 13. Apparatus as in claim 12 wherein thebiasing devices comprise resiliently urged guide pins and said pinsincorporate ends having stepped surfaces cooperating with adjacentsurfaces of the apparatus to act as flush pin gages indicating thecondition of elements loaded into the apparatus.
 14. Apparatus as inclaim 10 wherein the force applying means includes a hydraulic actuatorfor transmitting the applied force.
 15. Apparatus as in claim 14 whereinthe force applying means further includes a hardened hollow bushingengageable with said shaft opposite end and carried in a movable backupblock for transmitting to the shaft forces applied by the hydraulicactuator.
 16. Apparatus as in claim 10 wherein the force applying meansincludes a mechanical actuator for transmitting the applied force. 17.Apparatus as in claim 16 wherein the force applying means comprises ascrew actuator.
 18. Apparatus as in claim 17 wherein the force applyingmeans further includes a hardened hollow bushing engageable with saidshaft opposite end and carried in a movable backup block fortransmitting to the shaft forces applied by the screw actuator.